# Define here the models for your spider middleware
#
# See documentation in:
# https://docs.scrapy.org/en/latest/topics/spider-middleware.html

from scrapy import signals
import random

# useful for handling different item types with a single interface
from itemadapter import is_item, ItemAdapter

# 爬虫中间件 
# class MiddleSpiderMiddleware:
#     # Not all methods need to be defined. If a method is not defined,
#     # scrapy acts as if the spider middleware does not modify the
#     # passed objects.

#     @classmethod
#     def from_crawler(cls, crawler):
#         # This method is used by Scrapy to create your spiders.
#         s = cls()
#         crawler.signals.connect(s.spider_opened, signal=signals.spider_opened)
#         return s

#     def process_spider_input(self, response, spider):
#         # Called for each response that goes through the spider
#         # middleware and into the spider.

#         # Should return None or raise an exception.
#         return None

#     def process_spider_output(self, response, result, spider):
#         # Called with the results returned from the Spider, after
#         # it has processed the response.

#         # Must return an iterable of Request, or item objects.
#         for i in result:
#             yield i

#     def process_spider_exception(self, response, exception, spider):
#         # Called when a spider or process_spider_input() method
#         # (from other spider middleware) raises an exception.

#         # Should return either None or an iterable of Request or item objects.
#         pass

#     def process_start_requests(self, start_requests, spider):
#         # Called with the start requests of the spider, and works
#         # similarly to the process_spider_output() method, except
#         # that it doesn’t have a response associated.

#         # Must return only requests (not items).
#         for r in start_requests:
#             yield r

#     def spider_opened(self, spider):
#         spider.logger.info('Spider opened: %s' % spider.name)


# 下载中间件
class MiddleDownloaderMiddleware:
    # Not all methods need to be defined. If a method is not defined,
    # scrapy acts as if the downloader middleware does not modify the
    # passed objects.
    
    user_agent_list = [] # UA池
    # 代理池
    proxy_http = []
    proxy_https = []

    # 用于拦截请求 此时请求是从引擎发送到下载器 还没有被执行
    def process_request(self, request, spider):
        # Called for each request that goes through the downloader
        # middleware.

        # Must either:
        # - return None: continue processing this request
        # - or return a Response object
        # - or return a Request object
        # - or raise IgnoreRequest: process_exception() methods of
        #   installed downloader middleware will be called
        
        # 可以在这里进行UA伪装 和代理的使用 代理一般在处理异常请求中使用
        request.headers['User-Agent'] = random.choice(self.user_agent_list)
        # request.meta["proxy"] = random.choice(self.proxy_http)
        return None

    # 用于拦截响应数据 已经执行
    def process_response(self, request, response, spider):
        # Called with the response returned from the downloader.

        # Must either;
        # - return a Response object
        # - return a Request object
        # - or raise IgnoreRequest
        return response

    # 用于拦截异常请求 处理后重新提交请求
    def process_exception(self, request, exception, spider):
        # Called when a download handler or a process_request()
        # (from other downloader middleware) raises an exception.

        # Must either:
        # - return None: continue processing this exception
        # - return a Response object: stops process_exception() chain
        # - return a Request object: stops process_exception() chain
        
        # 对异常请求更换代理 
        # 判断http协议类型
        if request.url.split(':')[0] == 'http':
            request.meta['proxy'] = random.choice(self.proxy_http)
        else:
            request.meta['proxy'] = random.choice(self.proxy_https)
            
        # 必须返回请求才能重新发送 ！！！
        return request 

    # def spider_opened(self, spider):
    #     spider.logger.info('Spider opened: %s' % spider.name)
